QR codes are everywhere these days, from being printed onto receipts to chiseled into granite tombstones. [Will] came up with a way to modify existing QR codes, and his hack has the potential to cause quite a bit of harmless mischief.
[Will]‘s hack involves a little photo editing, transparency film, and some white-out/Liquid Paper/Tippex. After the ‘target’ and ‘destination’ QR codes have been imported into Gimp, the differences are found and the result printed out on a transparency sheet. After that, hang the transparency over the original and the QR code now goes to the URL of your choice.
On a ‘high’ level of error correction, a lot of neat stuff can be done with the design of a QR code including putting logos inside a QR code by modifying the 359 ‘data pixels’ of a 25×25 code. We’re wondering if anyone has ever written a script to exploit the error correction of QR codes. In any event, it is possible to brute-force changes until the least number of pixels are changed.
The ISO 18004 standard is available online if anyone would like to take up that challenge. If a Hack A Day reader figures it out, send in the code on the tip line and we’ll put that right up.